Methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most dangerous infectious agents in the U.S. and elsewhere, with a higher mortality rate than HIV-AIDS. MRSA is a strain of Staphylococcus aureus (S. aureus) bacteria, a common type of bacteria that may live on the skin and in the nasal passages of healthy people. MRSA does not respond to some of the antibiotics generally used to treat staphylococcus and other bacterial infections.
Healthcare-associated MRSA (HA-MRSA) infections occur in people who are or have recently been in a hospital or other health-care facility. Many people may be at risk of MRSA infection due to receiving healthcare services in an environment where the MRSA bacteria are colonized on surfaces, healthcare workers, inpatients or outpatients. Community-associated MRSA (CA-MRSA) infections occur in otherwise healthy people who have not recently been in the hospital. In fact, MRSA has become a primary cause of skin and soft tissue infections among persons without extensive exposure to healthcare settings, and the outbreaks have occurred in athletic team facilities, correctional facilities, and military basic training camps.
Pulsed-field gel electrophoresis (PFGE) is a molecular method for typing MRSA. It is used to identify index strain(s) of an outbreak or understand the clonal relationship among strains. The nonlimiting PFGE reference strains include USA100, USA200, USA300, USA400, USA500, USA600, USA700, USA800, USA1100 (see Network on Antimicrobial resistance in S. aureus (NARSA), available at UTL: narsa.net/). However, many isolates of MRSA are indistinguishable when compared using the standard PFGE typing method. This may present a problem when investigating local outbreaks of MRSA transmission in a healthcare setting.
Strains that are identified as belonging to the USA100, USA300, and USA600 strain types have specific clinical relevance. USA100 type strains are more likely to be HA-MRSA strains, typically have increased multi-drug resistance, and are not thought to be as virulent as USA300 type strains. USA300 type strains are more likely to be CA-MRSA, are less multi-drug resistant than USA100 strains, and typically have increased virulence. USA600 has been found to be associated with a higher than average mortality rate for MRSA, especially when associated with blood-stream infections.
Microbiological identification systems are based on different analytical techniques, such as phenotypic, genotypic, and strain typing. Each system has limitations due to method and/or database limitations and shortcomings in terms of accuracy, reproducibility, technical complexity, speed, and cost. Considering these limitations and the level of identification required as to genus, species, and strain, there is an ongoing need for strain typing technology to link cases together and identify sources of infection using more rapid and informative tests with a high level of accuracy. With such an invention, it would be possible to rapidly identify individuals who are colonized with MRSA, and thus interventions for MRSA colonization through decolonization, isolation procedures, or restrictions in occupational activities among clinicians and patients would be more effective.